Wind turbine technology is providing an ever-increasing proportion of the electrical energy generated in the United States and worldwide. Wind turbines transform kinetic energy, provided by a wind source, into mechanical energy, which may in turn be used to produce electricity. A typical wind turbine consists of an electrical generator mounted in a nacelle atop a tower that may be sixty (60) or more meters tall. The generator is powered by wind, which rotates the turbine blades, which are connected to a drive train assembly, the drive train assembly including a main shaft connected to the blades, a main shaft bearing, and a gear box which increases the shaft speed passed to the generator. Like the generator, the drive train assembly is usually mounted in the nacelle. It is well understood that one method for increasing the rated electrical output of a wind turbine is to increase the diameter of the main shaft, which may well exceed a diameter of one (1) meter. As turbines are manufactured with larger main shafts, the other components in the nacelle may necessarily also increase in size, including the nacelle itself.
As with most mechanical machinery, periodic maintenance, refurbishing or repair is needed for wind turbines, including the main shaft bearing. Presently, whenever a main bearing fails or otherwise requires replacement or maintenance, a large crane is used to first retract the nacelle roof, then remove an associated rotor assembly, and lastly extract the entire drive train assembly. When the drive train assembly reaches the ground, the gearbox may be unmated from the main shaft. The main shaft and main bearing are then sent to a repair shop to remove the old bearing and install a new one, often through a press-fit method. The main shaft with the new main bearing may then be mated with the gearbox, and then the crane will install the repaired drive train assembly into the nacelle. The process of removing the entire drive train assembly requires a large crane, which is itself difficult and costly to install. Additional time and expense is incurred by transporting the drive train assembly to an off-site location. Thus, a method for replacing the main bearing uptower is desired, particularly in larger turbines.